Coupling device and method of manufacturing coupling device

Title: Coupling device and method of manufacturing coupling device.Abstract: This coupling device includes a magnet rotator and a yoke-side member, while a conductor portion of the yoke-side member has a plurality of first conductor portions at least on a side opposed to magnets. A yoke of the yoke-side member is arranged at least on the side opposed to the magnets in a clearance between the plurality of first conductor portions. The ratio of the circumferential length of each of the first conductor portions to the circumferential length of the yoke is at least 1/1.4. ...

CROSS-REFERENCE TO RELATED APPLICATIONS

The priority application numbers JP2010-113320, Coupling Device, May 17, 2010, Hiromitsu Ohhashi and Junichi Sutani, upon which this patent application is based are hereby incorporated by reference. This application is a continuation of PCT/JP2011/60961, Coupling Device, May 12, 2011, Hiromitsu Ohhashi and Junichi Sutani.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a coupling device and a method of manufacturing a coupling device, and more particularly, it relates to a coupling device including a magnet rotator and a yoke-side member coupled to the magnet rotator and a method of manufacturing a coupling device.

2. Description of the Background Art

A coupling device including a magnet rotator and a yoke-side member coupled to the magnet rotator is known in general, as disclosed in Japanese Patent Laying-Open No. 8-135682 (1996), for example.

Japanese Patent Laying-Open No. 8-135682 discloses a starting device (coupling device) including a discoidal (disk-shaped) driving member (magnet rotator) including a plurality of permanent magnets so arranged that different magnetic poles alternately line up in a circumferential direction and a discoidal driven member (yoke-side member) arranged to be opposed to the permanent magnets of the driving member. The driven member of the starting device described in Japanese Patent Laying-Open No. 8-135682 is constituted of a conductive member (conductor portion) provided with a plurality of through-holes on positions opposed to the permanent magnets and a core member (yoke), having projecting portions corresponding to the through-holes, arranged on a side of the conductive member opposite to the driving member. The core member passes through the through-holes of the conductive member so that end surfaces of the projecting portions approach the permanent magnets, thereby increasing the amount of magnetic flux passing through the projecting portions (through-holes) of the core member. Thus, the amount of eddy current flowing in the conductive member is so increased that a relatively high torque can be generated in the driven member. In order to generate a higher torque in the driven member, the amount of generated eddy current must conceivably be increased by increasing the areas of portions of the driving member and the driven member opposed to each other.

In the starting device disclosed in Japanese Patent Laying-Open No. 8-135682, however, both of the driving member and the driven member are discoidal, and hence the sizes of the discoidal driving member and the discoidal driven member must be both radially increased in order to increase the areas of the portions of the driving member and the driven member opposed to each other. Therefore, the size of the starting device disclosed in Japanese Patent Laying-Open No. 8-135682 is disadvantageously radially increased due to the radial increase of the sizes of the discoidal driving member and the discoidal driven member.

SUMMARY

OF THE INVENTION

The present invention has been proposed in order to solve the aforementioned problem, and an object of the present invention is to provide a coupling device and a method of manufacturing a coupling device each allowing generation of a higher torque while suppressing radial size increase of the coupling device.

A coupling device according to a first aspect of the present invention includes a cylindrical magnet rotator including magnets so arranged that different magnetic poles alternately line up in a circumferential direction and a cylindrical yoke-side member, including a conductor portion made of a nonmagnetic material and a yoke, arranged on the inner side or the outer side of the magnet rotator to be relatively rotatable in a state not in contact with the magnet rotator, while the conductor portion of the yoke-side member has a plurality of first conductor portions arranged to extend in a direction of the axis of rotation at a prescribed interval in the circumferential direction at least on a side opposed to the magnets, the yoke of the yoke-side member is at least arranged on the side opposed to the magnets in a clearance between the plurality of the first conductor portions, and the ratio between the circumferential length of each of the first conductor portions and the circumferential length of the yoke arranged in the clearance between the first conductor portions (circumferential length of each first conductor portion/circumferential length of yoke) is at least 1/1.4.

As hereinabove described, the coupling device according to the first aspect of the present invention is provided with the cylindrical magnet rotator including the magnets and the cylindrical yoke-side member arranged on the inner side or the outer side of the magnet rotator to be relatively rotatable in the state not in contact with the magnet rotator, whereby areas of portions of the magnet rotator and the yoke-side member opposed to each other can be increased by forming both of the cylindrical yoke-side member and the cylindrical magnet rotator to extend in the direction of the axis of rotation. Thus, the sizes of the magnet rotator and the yoke-side member may not be radially increased in order to increase the areas of the portions of the magnet rotator and the yoke-side member opposed to each other, whereby the coupling device can be inhibited from being radially increased in size for generating a higher torque.

Further, the yoke is so arranged on the side opposed to the magnets in the clearance between the plurality of first conductor portions that the same can more approach the magnets as compared with a case where the conductor portion is provided on the side opposed to the magnets to cover the whole yoke. Thus, the amount of magnetic flux generated in the yoke can be increased, whereby the amount of eddy current flowing in the first conductor portions can be increased. In addition, the ratio between the circumferential length of each of the first conductor portions and the circumferential length of the yoke (circumferential length of each first conductor portion/circumferential length of yoke) is so set to at least 1/1.4 that sectional areas of the first conductor portions in the circumferential direction can be increased, whereby electric resistance of the first conductor portions can be reduced. Thus, the amount of the eddy current flowing in the first conductor portions can be increased. In a case of a transmission system transmitting rotational force to the yoke-side member through eddy current, therefore, a torque generated in the yoke-side member can be increased. In a case of a braking system generating braking force in the yoke-side member through eddy current, on the other hand, the amount of generated Joule heat (Joule loss) can be increased, whereby the coupling device can generate higher braking force.

In the aforementioned coupling device according to the first aspect, the ratio between the circumferential length of each of the first conductor portions and the circumferential length of the yoke arranged in the clearance between the first conductor portions is preferably not more than 3.4/1. If the ratio between the circumferential length of each of the first conductor portions and the circumferential length of the yoke is greater than 3.4/1, the amount of magnetic flux passing through the clearance between the first conductor portions does not increase beyond a prescribed value due to saturation of magnetic flux, generated from the magnets, in the yoke. Therefore, the amount of eddy current generated in the yoke-side member (first conductor portions) is reduced. When the ratio between the circumferential length of each of the first conductor portions and the circumferential length of the yoke is set to not more than 3.4/1 as described above, on the other hand, the magnetic flux generated from the magnets can be inhibited from being saturated in the yoke, whereby the amount of the eddy current flowing in the first conductor portions can be inhibited from reduction.

In this case, the ratio between the circumferential length of each of the first conductor portions and the circumferential length of the yoke arranged in the clearance between the first conductor portions is preferably at least 1/1 and not more than 2.1/1. According to this structure, the torque and the amount of Joule heat can be more increased, and the amount of the eddy current flowing in the first conductor portions can be more inhibited from reduction.

In the aforementioned coupling device exhibiting the ratio between the circumferential lengths set to at least 1/1 and not more than 2.1/1, the ratio between the circumferential length of each of the first conductor portions and the circumferential length of the yoke arranged in the clearance between the first conductor portions is preferably at least 1.2/1 and not more than 1.8/1. According to this structure, the torque and the amount of Joule heat can be more increased, and the amount of the eddy current flowing in the first conductor portions can be effectively inhibited from reduction.

In the aforementioned coupling device according to the first aspect, the radial thickness of the first conductor portions is preferably in excess of the radial thickness of the magnets. According to this structure, sectional areas of the first conductor portions in the circumferential direction can be increased, whereby electric resistance of the first conductor portions can be reduced. Thus, the amount of the eddy current flowing in the first conductor portions can be increased.

In the aforementioned coupling device according to the first aspect, the plurality of first conductor portions are preferably formed to extend in the direction of the axis of rotation in a state arranged at substantially equal intervals in the circumferential direction. According to this structure, eddy current generated in each of the plurality of first conductor portions can be fed along the direction of the axis of rotation in a substantially uniform state, whereby a substantially uniform torque and substantially uniform Joule heat can be generated not only in the circumferential direction but also in the direction of the axis of rotation.

In the aforementioned coupling device according to the first aspect, the conductor portion of the yoke-side member preferably further has an annular second conductor portion arranged on end portions of the plurality of first conductor portions in the direction of the axis of rotation for connecting the plurality of first conductor portions with each other. According to this structure, the second conductor portion can electrically connect the plurality of first conductor portions with each other. Thus, eddy current can be generated between different ones of the first conductor portions. Further, the second conductor portion is arranged on the end portions of the plurality of first conductor portions in the direction of the axis of rotation, whereby the length in the direction of the axis of rotation where the eddy current flows can be increased as compared with a case where no second conductor portion is arranged on the end portions. Thus, a torque and Joule heat can be generated in the yoke-side member in a wider range in the direction of the axis of rotation, whereby the torque and the amount of Joule heat in the yoke-side member can be further increased.

In this case, the second conductor portions are preferably arranged on both end portions of the first conductor portions in the direction of the axis of rotation respectively. According to this structure, the second conductor portions provided on both end portions respectively connect the plurality of first conductor portions with each other, whereby the coupling device can be so formed that eddy current flows between different ones of the first conductor portions and the second conductor portions provided on both end portions. Thus, a torque and Joule heat can be generated in the yoke-side member in a wider range in the direction of the axis of rotation.

In the aforementioned coupling device including the conductor portion having the second conductor portion, the second conductor portion is preferably formed integrally with the plurality of first conductor portions. According to this structure, contact resistance between the plurality of first conductor portions and the second conductor portion can be reduced, whereby higher eddy current can be generated in the conductor portion.

In the aforementioned coupling device according to the first aspect, a plurality of groove portions or a plurality of hole portions are preferably formed in the vicinity of a surface of the yoke opposed to the magnets to extend in the direction of the axis of rotation, and each of the plurality of first conductor portions is preferably arranged in each of the plurality of groove portions or the plurality of hole portions. According to this structure, the plurality of first conductor portions extending in the direction of the axis of rotation at the prescribed interval in the circumferential direction can be easily formed by simply arranging each of the plurality of first conductor portions in each of the plurality of groove portions or the plurality of hole portions extending in the direction of the axis of rotation.

In the aforementioned coupling device according to the first aspect, at least either the magnet rotator or the yoke-side member is preferably formed to be capable of changing the areas of portions of the magnets of the magnet rotator and the yoke-side member opposed to each other. According to this structure, increase/decrease of the amount of the eddy current flowing in the first conductor portions can be so varied that a torque and Joule heat in the coupling device can be more correctly controlled by controlling the magnitude of the eddy current.

In this case, either the magnet rotator or the yoke-side member is preferably formed to change the areas of the portions of the magnets of the magnet rotator and the yoke-side member opposed to each other by moving with respect to either the yoke-side member or the magnet rotator in the direction of the axis of rotation. According to this structure, the areas of the portions of the magnets of the magnet rotator and the yoke-side member opposed to each other can be easily varied.

A method of manufacturing a coupling device according to a second aspect of the present invention is a method of manufacturing a coupling device including a cylindrical magnet rotator including magnets so arranged that different magnetic poles alternately line up in a circumferential direction and a cylindrical yoke-side member, including a conductor portion made of a nonmagnetic material and a yoke, arranged on the inner side or the outer side of the magnet rotator to be relatively rotatable in a state not in contact with the magnet rotator, including steps of preparing a plurality of discoidal yoke plate members each provided with a plurality of outer holes in the vicinity of the outer periphery thereof, forming a cylindrical yoke extending in a direction of the axis of rotation so that a hole portion constituted of the outer holes extends in the direction of the axis of rotation by stacking the plurality of yoke plate members, and forming the yoke-side member by forming a plurality of first conductor portions of the conductor portion made of the nonmagnetic material in the hole portion of the yoke.

In the method of manufacturing a coupling device according to the second aspect of the present invention, as hereinabove described, the yoke-side member is formed by forming the plurality of first conductor portions of the conductor portion made of the nonmagnetic material in the hole portion of the cylindrical yoke so that both of the cylindrically formed yoke-side member and the cylindrical magnet rotator can be arranged to extend in the direction of the axis of rotation, whereby areas of portions of the magnet rotator and the yoke-side member opposed to each other can be increased. Thus, the sizes of the magnet rotator and the yoke-side member may not be radially increased in order to increase the areas of the portions of the magnet rotator and the yoke-side member opposed to each other, whereby the coupling device can be inhibited from being radially increased in size for generating a higher torque.

Further, the plurality of first conductor portions of the conductor portion made of the nonmagnetic material are formed in the hole portion of the yoke, whereby the yoke can more approach the magnets as compared with a case where the conductor portion is provided on the side opposed to the magnets to cover the whole yoke. Thus, the amount of magnetic flux generated in the yoke can be increased, whereby the amount of eddy current flowing in the first conductor portions can be increased. In a case of a transmission system transmitting rotational force to the yoke-side member through eddy current, therefore, a torque generated in the yoke-side member can be increased. In a case of a braking system generating braking force in the yoke-side member through eddy current, on the other hand, the amount of generated Joule heat (Joule loss) can be increased, whereby the coupling device can generate higher braking force.

In the aforementioned method of manufacturing a coupling device according to the second aspect, the step of forming the yoke-side member preferably includes a step of casting the plurality of first conductor portions of the conductor portion made of the nonmagnetic material by casting the nonmagnetic material into the hole portion of the yoke. According to this structure, the plurality of first conductor portions of the conductor portion made of the nonmagnetic material can be easily provided on the yoke-side member.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a coupling device according to a first embodiment of the present invention;

FIG. 2 is a plan view of the coupling device according to the first embodiment of the present invention as viewed along arrow X2 in FIG. 1;

FIG. 3 is a perspective view showing a load-side rotator of the coupling device according to the first embodiment of the present invention;

FIG. 4 is a sectional view showing a state of stacking a yoke in a step of manufacturing a load-side rotating portion of the coupling device according to the first embodiment of the present invention;

FIG. 5 is a sectional view showing a state of die-casting a conductor portion in another step of manufacturing the load-side rotating portion of the coupling device according to the first embodiment of the present invention;

FIG. 6 is a sectional view showing a state of removing a die in still another step of manufacturing the load-side rotating portion of the coupling device according to the first embodiment of the present invention;

FIG. 7 is a sectional view showing a state of cutting the outer peripheral surface of the yoke in a further step of manufacturing the load-side rotating portion of the coupling device according to the first embodiment of the present invention;

FIG. 8 is a plan view showing a coupling device according to comparative example;

FIG. 9 is a schematic diagram showing a measuring system employed for confirmatory experiments conducted in order to confirm effects of the coupling device according to the first embodiment of the present invention;

FIG. 10 is a table showing torques with respect to relative rotational frequencies in coupling devices according to Example 1 and comparative example 1 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 11 is a graph showing the torques with respect to the relative rotational frequencies in the coupling devices according to Example 1 and comparative example 1 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 12 is a table showing Joule losses with respect to torques in the coupling devices according to Example 1 and comparative example 1 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 13 is a graph showing the Joule losses with respect to the torques in the coupling devices according to Example 1 and comparative example 1 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 14 is a table showing Joule losses with respect to relative rotational frequencies in the coupling devices according to Example 1 and comparative example 1 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 15 is a graph showing the Joule losses with respect to the relative rotational frequencies in the coupling devices according to Example 1 and comparative example 1 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 16 is a table showing torques with respect to relative rotational frequencies in coupling devices according to Examples 2 to 8 and comparative example 2 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 17 is a graph showing the torques with respect to the relative rotational frequencies in the coupling devices according to Examples 2 to 8 and comparative example 2 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 18 is a table showing torques with respect to relative rotational frequencies in coupling devices according to Examples 4 and 9 and comparative example 2 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 19 is a graph showing the torques with respect to the relative rotational frequencies in the coupling devices according to Examples 4 and 9 and comparative example 2 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 20 is a table showing torques with respect to relative rotational frequencies in coupling devices according to Examples 10 and 11 and comparative examples 3 and 4 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 21 is a graph showing the torques with respect to the relative rotational frequencies in the coupling devices according to Examples 10 and 11 and comparative examples 3 and 4 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 22 is a table showing Joule losses with respect to torques in the coupling devices according to Examples 10 and 11 and comparative examples 3 and 4 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 23 is a graph showing the Joule losses with respect to the torques in the coupling devices according to Examples 10 and 11 and comparative examples 3 and 4 in the confirmatory experiments conducted in order to confirm the effects of the coupling device first embodiment of the present invention;

FIG. 24 is a table showing Joule losses with respect to relative rotational frequencies in the coupling devices according to Examples 10 and 11 and comparative examples 3 and 4 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 25 is a graph showing the Joule losses with respect to the relative rotational frequencies in the coupling devices according to Examples 10 and 11 and comparative examples 3 and 4 in the confirmatory experiments conducted in order to confirm the effects of the coupling device according to the first embodiment of the present invention;

FIG. 26 is a sectional view showing a coupling device according to a second embodiment of the present invention;

FIG. 27 is a plan view of the coupling device according to the second embodiment of the present invention as viewed along arrow X2 in FIG. 26;

FIG. 28 is a plan view showing a state of changing a relative position of a switch member shown in FIG. 27 with respect to a motor-side rotator; and

FIG. 29 is a sectional view showing a coupling device according to a modification of the first embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are now described with reference to the drawings.

First Embodiment

First, the structure of a coupling device 1 according to a first embodiment of the present invention is described with reference to FIGS. 1 to 3.

The coupling device 1 according to the first embodiment of the present invention is formed by a magnet-side portion 10 and a yoke-side portion 20, as shown in FIG. 1. The magnet-side portion 10 includes a shaft portion 10a having a first end portion (along arrow X1) connected to a motor (not shown) and a magnet-side rotator 30 provided on a second end portion (along arrow X2) of the shaft portion 10a. The yoke-side portion 20 includes a shaft portion 20a having a first end portion (along arrow X2) connected to a load portion (not shown) formed by a driving portion or the like and a yoke-side member 40 provided on a second end portion of the shaft portion 20a. In other words, the magnet-side portion 10 is connected to the side of the motor, while the yoke-side portion 20 is connected to the side of the load portion. The shaft portions 10a and 20a are formed to rotate on a substantially identical axis 300 of rotation extending in a direction X. The magnet-side rotator 30 is an example of the “magnet rotator” in the present invention.

The magnet-side portion 10 may be connected not to the side of the motor but to the side of the load portion, while the yoke-side portion 20 may be connected not to the side of the load portion but to the side of the motor. The following description is made on the premise that the magnet-side portion 10 is connected to the side of the motor and the yoke-side portion 20 is connected to the side of the load portion.

The magnet-side rotator 30 is made of a ferromagnetic material such as general carbon steel such as SS400, and has a portion provided in the form of a concave cylinder along arrow X2. The magnet-side rotator 30 has a shaft hole portion 30a receiving the shaft portion 10a. The coupling device 1 is so formed that the shaft portion 10a is so inserted into the shaft hole portion 30a that the magnet-side rotator 30 also rotates on the axis 300 of rotation following rotation of the shaft portion 10a. The inner diameter L1 of a concave inner peripheral surface 30b of the magnet-side rotator 30 is about 90 mm, while the outer diameter L2 of the magnet-side rotator 30 is about 102 mm.

As shown in FIG. 2, 12 magnets 31 are so arranged on the magnet-side rotator 30 that different magnetic poles alternately line up along the circumferential direction of the concave inner peripheral surface 30b. The 12 magnets 31 are arranged to extend parallelly to the axis 300 of rotation, as shown in FIG. 1.

More specifically, the 12 magnets 31 are constituted of magnets 31a having north poles arranged on the side of the axis 300 (see FIG. 1) of rotation and magnets 31b having south poles arranged on the side of the axis 300 of rotation, as shown in FIG. 2. The magnets 31a and 31b are arranged to alternately line up on the concave inner peripheral surface 30b of the magnet-side rotator 30 along the circumferential direction at substantially equiangular intervals (about 30°). FIG. 2 illustrates only the magnetic poles on the side of the axis 300 of rotation, and omits illustration of a short-circuit portion 42b, described later, along arrow X2. The 12 magnets 31 have a radial thickness W1 of about 5 mm, as shown in FIG. 1. The coupling device 1 is so formed that magnetic flux flows between the magnets 31a and the magnets 31b adjacent thereto, as shown in FIG. 2.

The yoke-side member 40 is formed to be rotatable on the axis 300 of rotation, and provided in the form of a cylinder. Further, the yoke-side member 40 is arranged on the inner side of the magnet-side rotator 30 provided with the 12 magnets 31, and formed to be relatively rotatable while being coupled to the magnet-side rotator 30 at a prescribed interval in a state not in contact with the magnet-side rotator 30. The interval (clearance) between the yoke-side member 40 and the magnet-side rotator 30 is about 1 mm.

The yoke-side member 40 is constituted of a yoke 41 formed by stacking silicon steel plates and a conductor portion 42 made of an alloy mainly containing Al or Cu, which is a nonmagnetic material. The silicon steel plates are made of an Si-containing Fe alloy, which is a ferromagnetic material easily transmitting magnetic flux (having high magnetic permeability). The yoke 41 is provided in the form of a cylinder having an outer diameter L3 of about 78 mm and a length L4 of about 60 mm in the direction X, as shown in FIG. 1. The yoke 41 has a shaft hole portion 41a receiving the shaft portion 20a. The coupling device 1 is so formed that the shaft portion 20a is so inserted into the shaft hole portion 41a that the yoke 41 (yoke-side member 40) also rotates on the axis 300 of rotation following rotation of the shaft portion 20a. An outer peripheral surface 41b of the yoke 41 is arranged to be opposed to the 12 magnets 31 arranged on the inner peripheral surface 30b of the magnet-side rotator 30.

As shown in FIG. 2, 44 groove portions 41c are arranged on the outer peripheral surface 41b of the yoke 41 at substantially equal angles (about 8.2°), and formed to extend in the extensional direction (direction X in FIG. 1) of the axis 300 of rotation. In other words, the coupling device 1 is so formed that 44 projecting portions 41d provided with no groove portions 41c are positioned in clearances between the groove portions 41c respectively. The projecting portions 41d are sectorially formed in plan view, and the coupling device 1 is so formed that an angle θ1 between both outer side surfaces of each sectorial projecting portion 41d is about 3.7°. Further, the coupling device 1 is so formed that an angle θ2 between both inner side surfaces of each groove portion 41c is about 4.5°. Thus, the coupling device 1 is so formed that the length of the outer periphery of each projecting portion 41d is about 0.802 mm (78 mm×3.7°/360° and the length of the outer periphery of a portion provided with each groove portion 41c is about 0.975 mm (78 mm×4.5°/360°. In other words, the coupling device 1 is so formed that the length of the outer periphery of each groove portion 41c is about 1.2 times the length of the outer periphery of each projecting portion 41d.

As shown in FIG. 3, the coupling device 1 is so formed that the 44 groove portions 41c are inclined (skewed) with respect to the axis 300 of rotation extending in the direction X at an angle θ3. The 44 groove portions 41c have a radial depth of about 9 mm.

According to the first embodiment, the conductor portion 42 is constituted of 44 axial conductor portions 42a (see FIG. 2) arranged on the 44 groove portions 41c of the yoke 41 respectively and a pair of short-circuit portions 42b formed on both end portions of the yoke 41 and the axial conductor portions 42a in the direction X respectively. The axial conductor portions 42a are formed to extend in the extensional direction (direction X) of the axis 300 of rotation. The axial conductor portions 42a are examples of the “first conductor portions” in the present invention, and the short-circuit portions 42b are examples of the “second conductor portion” in the present invention.

The axial conductor portions 42a are arranged from the vicinity of the outer peripheral surface 41b of the yoke 41 up to bottom portions of the groove portions 41c on the side of the axis 300 of rotation respectively, as shown in FIG. 2. Thus, the conductor portion 42 has a thickness W2 (see FIG. 1) of about 9.0 mm in the radial direction. Therefore, the coupling device 1 is so formed that the radial thickness W2 (about 9.0 mm) of the conductor portion 42 is about 1.8 times the radial thickness W1 (about 5.0 mm) of the magnets 31. Further, the coupling device 1 is so formed that the length (about 0.975 mm) of the outer periphery of each groove portion 41c where the corresponding axial conductor portion 42a is arranged is about 1.2 times the length (about 0.802 mm) of the outer periphery of each projecting portion 41d of the yoke 41 as described above, whereby the length of the outer periphery of each axial conductor portion 42a is about 1.2 times the length of the outer periphery of each projecting portion 41d of the yoke 41.

As shown in FIG. 3, the coupling device 1 is so formed that the 44 groove portions 41c are inclined with respect to the axis 300 of rotation extending in the direction X at the angle θ3, whereby the 44 axial conductor portions 42a are also inclined with respect to the axis 300 of rotation extending in the direction X at the angle θ3. The projecting portions 41d of the yoke 41 are arranged between the 44 axial conductor portions 42a arranged on the 44 groove portions 41c.

The pair of short-circuit portions 42b are arranged on end portions of the 44 axial conductor portions 42a along arrows X1 and X2 respectively. In other words, the pair of short-circuit portions 42b are arranged to hold the 44 axial conductor portions 42a and the yoke 41 therebetween from both sides in the direction X. Further, the pair of short-circuit portions 42b are annularly formed to connect the 44 axial conductor portions 42a with each other in the circumferential direction. The 44 axial conductor portions 42a and the pair of short-circuit portions 42b are integrally formed. The radial thickness L5 (see FIG. 1) of the pair of short-circuit portions 42b is about 10 mm.

The coupling device 1 is so formed that magnetic flux from the magnets 31 changes on the projecting portions 41d of the yoke 41 upon rotation of the magnet-side rotator 30. Further, the coupling device 1 is so formed that eddy current is generated in the 44 axial conductor portions 42a and the pair of short-circuit portions 42b on the basis of this change of the magnetic flux. In addition, the coupling device 1 is so formed that force acting in the same direction of rotation as that of the magnet-side rotator 30 is applied to each of the 44 axial conductor portions 42a due to the eddy current to relatively rotate the yoke-side member 40 in the same direction of rotation as the magnet-side rotator 30 in the state not in contact with the magnet-side rotator 30. At this time, rotational frequency difference (relative rotational frequency) is caused between the rotational frequencies of the magnet-side rotator 30 and the yoke-side member 40, thereby causing difference between energy supplied from the magnet-side rotator 30 and that transmitted to the yoke-side member 40. Energy corresponding to this difference is converted to force and heat, thereby generating a torque and Joule heat in the yoke-side member 40.

However, the yoke-side member 40 may not rotate with respect to the magnet-side rotator 30 when the force acting in the same direction of rotation as that of the magnet-side rotator 30 is applied to each of the 44 axial conductor portions 42a due to the eddy current. The coupling device 1 is so formed that Joule heat is generated in the yoke-side member 40 in this case.

The coupling device 1 is so formed that the eddy current flows through a loop-shaped path constituted of two axial conductor portions 42a and the pair of short-circuit portions 42b.

A method of manufacturing the yoke-side member 40 of the coupling device 1 according to the first embodiment of the present invention is now described with reference to FIGS. 3 to 7.

First, discoidal silicon steel plates (not shown) each having a thickness of about 0.5 mm are prepared. Each discoidal silicon steel plate has a central hole, corresponding to the axial hole portions 41a, provided at the center thereof and 44 outer holes, corresponding to the 44 groove portions 41c, provided in the vicinity of the outer periphery thereof. Then, about 120 discoidal silicon steel plates are so stacked as to form the cylindrical yoke 41 having the shaft hole portion 41a and extending in the extensional direction (direction X) of the axis 300 of rotation, as shown in FIG. 4. At this time, the silicon steel plates are so stacked that 44 hole portions 41e constituted of the outer holes of about 120 silicon steel plates are inclined with respect to the axis 300 of rotation extending in the direction X at the angle θ3 (see FIG. 3). The silicon steel plates are examples of the “yoke plate members” in the present invention.

Thereafter dies 50 and 51 are arranged on the sides of the yoke 41 along arrows X1 and X2 respectively. The dies 50 and 51 are provided with die faces 50a and 51a for forming the short-circuit portions 42b along arrows X1 and X2 respectively. Further, the die 50 is provided with an injection hole 50b for injecting the alloy containing Al or Cu into the die faces 50a and 51a and the hole portions 41e of the yoke 41.

Then, the alloy, containing Al or Cu, heated to at least about 700° C. and not more than about 800° C. is injected into the die faces 50a and 51a and the hole portions 41e of the yoke 41 through the injection hole 50b as shown in FIG. 5, thereby casting the conductor portion 42 made of the alloy containing Al or Cu. At this time, the 44 axial conductor portions 42a of the conductor portion 42 are formed in the 44 hole portions 41e respectively, while the pair of short-circuit portions 42b of the conductor portion 42 are formed on the die faces 50a and 51a respectively. Thus, the 44 axial conductor portions 42a and the pair of short-circuit portions 42b are integrally formed.

Thereafter the dies 50 and 51 are detached from the sides of the yoke 41 along arrows X1 and X2 respectively, as shown in FIG. 6. Then, the outer peripheral surface 41b of the yoke 41 is cut by a prescribed amount for partially cutting the side surfaces of the 44 hole portions 41e, thereby forming the 44 groove portions 41c where the axial conductor portions 42a are individually arranged, as shown in FIG. 7. The yoke-side member 40 is formed in this manner.

According to the first embodiment, as hereinabove described, the coupling device 1 is provided with the cylindrical magnet-side rotator 30 including the 12 magnets 31 and the cylindrical yoke-side member 40 arranged on the inner side of the magnet-side rotator 30 to be covered with the concave inner peripheral surface 30b of the magnet-side rotator 30 and formed to be relatively rotatable in the state not in contact with the magnet-side rotator 30. Further, both of the magnet-side rotator 30 and the yoke-side member 40 are formed to extend in the extensional direction of the axis 300 of rotation and formed to rotate on the substantially identical axis 300 of rotation, whereby the areas of the portions of the magnet-side rotator 30 and the yoke-side member 40 opposed to each other can be increased. Thus, the sizes of the magnet-side rotator 30 and the yoke-side member 40 may not be increased in the radial direction in order to increase the areas of the portions of the magnet-side rotator 30 and the yoke-side member 40 opposed to each other, whereby the size of the coupling device 1 can be inhibited from being increased in the radial direction for generating a higher torque.

According to the first embodiment, as hereinabove described, the projecting portions 41d positioned on the side of the outer peripheral surface 41b of the yoke 41 are arranged on the side opposed to the 12 magnets 31, and arranged on between the 44 axial conductor portions 42a (groove portions 41c), whereby the yoke 41 can more approach the 12 magnets 31 as compared with a case where the conductor portion 42 is provided on the side of the outer peripheral surface 41b of the yoke 41 to cover the overall yoke 41. Thus, the amount of the magnetic flux generated in the yoke 41 can be further increased, whereby the amount of the eddy current flowing in the axial conductor portions 42a can be further increased. In a case of a transmission system transmitting rotational force to the yoke-side member 40 through the eddy current, therefore, the torque generated in the yoke-side member 40 can be further increased. In a case of a braking system generating braking force in the yoke-side member 40 through the eddy current, on the other hand, the amount of generated Joule heat (Joule loss) can be further increased, whereby the coupling device 1 can generate higher braking force.

According to the first embodiment, as hereinabove described, the 44 axial conductor portions 42a are formed to extend in the extensional direction oft the axis 300 of rotation in the state arranged at substantially equal angles (about 8.2°) in the circumferential direction so that the eddy current generated in the 44 axial conductor portions 42a can be fed along the extensional direction of the axis 300 of rotation in a substantially uniform state, whereby a substantially uniform torque and substantially uniform Joule heat can be generated not only in the circumferential direction but also in the extensional direction of the axis 300 of rotation.

According to the first embodiment, as hereinabove described, the coupling device 1 is so formed that the length (about 0.975 mm) of the outer peripheries of the axial conductor portions 42a is about 1.2 times the length (about 0.802 mm) of the outer peripheries of the projecting portions 41d of the yoke 41 so that sectional areas of the axial conductor portions 42a in the circumferential direction can be increased as compared with a case where the ratio between the length of the outer peripheries of the axial conductor portions 42a and that of the outer peripheries of the projecting portions 41d of the yoke 41 is set to be smaller than 1/1.4, whereby electric resistance of the axial conductor portions 42a can be reduced. Thus, the amount of the eddy current flowing in the axial conductor portions 42a can be increased, whereby the torque and the amount of the Joule heat can be more increased.

According to the first embodiment, as hereinabove described, the coupling device 1 is so formed that the length of the outer peripheries of the axial conductor portions 42a is about 1.2 times the length of the outer peripheries of the projecting portions 41d of the yoke 41 so that the magnetic flux generated from the 12 magnets 31 can be inhibited from being saturated on the projecting portions 41d of the yoke 41 as compared with a case where the ratio between the length of the outer peripheries of the axial conductor portions 42a and that of the outer peripheries of the projecting portions 41d of the yoke 41d is set to be greater than 3.4/1, whereby the amount of the eddy current flowing in the axial conductor portions 42a can be inhibited from reduction.

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